Pipe bending apparatus and method of bending



Oct. 14, 1969 v. GREGG 3,472,056

PIPE BENDING APPARATUS AND METHOD OF BENDING Filed Nov. 25, 1966 1.\'ENTOR.

United States Patent US. Cl. 72369 Claims ABSTRACT OF THE DISCLOSURE Thespecification and drawings describe and illustrate preferred embodimentsof apparatus and method for bending tubular articles. In the disclosedapparatus, a reciprocally supported ram die engages a tubular pipe thatis supported upon a pair of pivoted wing dies and bends the pipe into aradius defined by the shape of the ram die. The ram die is provided withat least one indentation in its surface so that the material of the pipeon the inside of the bend that is stressed in compression by the bendingwill permanently deform into this depression and form a localized,radially deflected portion in the bent pipe. Through the use of theindented portion of the die, random surface irregularities ordistortions that occur in normal bending operations are precluded. It isto be understood that the foregoing abstract of the disclosure is not tobe construed in interpreting the appended claims.

Background of the invention This invention relates to an apparatus forbending tubular articles and a method of bending tubular articles.

Often tubular articles such as pipe must be formed with a series ofradically different and acute bends. The manufacture of tail and exhaustpipes for automotive vehicles is a typical example where a pipe must beformed with such a series of bends in order to enable it to fit thespace allotted beneath the vehicle. When forming such pipes, accuracy ofbending, quality of bending and cost are all very critical factors.

In the normal method of bending tubular articles the tubular article ispositioned in engagement with an arcuate surface of the die and is bentto conform to this arcuate surface. When the pipe is thus bent, the material adjacent the die and on the inside of the bend is subject toconsiderable compressive stress and the material on the opposite side issubjected to tensile stress. Since automotive exhaust pipes generallyhave extremely thin wall sections to maintain low cost and minimumweight, it is common for the walls to collapse on the outside of thebend and wrinkle or fold on the inside of the bend during the formingoperation. This is because the bending stresses exceed greatly the yieldstrength of the material. Although some of these detrimental effects maybe avoided through the use of mandrels on the inside of the pipe, localsurface blemishes, commonly known as blisters, are formed adjacent theend of the mandrel or at locations spaced from the die. Laminated pipealso has the same defects when being bent as plain pipe bent with theassistance of a mandrel.

Summary of the invention The method and apparatus embodying thisinvention have been found to permit bending of pipe, particularlylaminated pipe, and relieves the compressive and tensile stresses on theinside and the outside of the bend, respectively, by causing controlleddeformations of the metal of the pipe on the inside of the bend. Morespecifically, the method embodying this invention is particularlyadapted to form an arcuate bend in a hollow tubular article and "iceprevent undesirable surface deformations due to the stresses produced inthe material of the article by the bending. The method comprises thesteps of permanently deforming the tubular article into an arcuate bendand employing the compressive stresses in the material on the inside ofthe bend generated by the bending to deform the material in a directiontransverse to the bend and at a preselected and predetermined location.

An apparatus embodying this invention includes at least one die having agenerally arcuate surface conforming to the shape of the desired bend.Transverse to the bend, the bending die is generally complementary in'shape to the cross-section of the tubular article to be bent and isformed with at least one surface discontinuity in the area that contactsthe pipe. This discontinuity acts to permit displacement of the metal ofthe pipe during bending at a controlled and preselected location.

Brief description of the drawings FIGURE 1 is a schematic front view ofa simplified bending apparatus of the type to which the presentinvention may be applied and shows the apparatus prior to bending of apipe.

FIGURE 2 is a view of the apparatus shown in FIG- URE 1, but shows theposition of the parts after a bend has been formed in the pipe.

FIGURE 3 is an enlarged front view of the ram die shown in FIGURE 1.

FIGURE 4 is a side elevational view of the die shown in FIGURE 1.

FIGURE 5 is a side view of the bent pipe.

FIGURE 6 is a side view of the form taken by a pipe where a bend isformed near the end of the pipe by previously known methods andapparatus.

FIGURE 7 is a partial side elevational view of a ram die formed toprevent the type of pipe deformation shown in FIGURE 6.

Description of preferred embodiments of the invention A bendingapparatus 1 is provided with a ram die 3 that is supported forreciprocation in a vertical direction as shown by the arrows 5 and isoperated by any suitable power source in a known manner. Supportedbeneath the ram die 3 are a pair of wing dies 7 land 9 that may swingabout pivot points 11 and 13. The ram die 3 and wing dies 7 and 9 havesurfaces that correspond generally to the surface of the tubular articleto be bent, in this case the bent article being :a cylindrical thin wallpipe 15. Thus, the ram die 3 has a channel 17 of semicircular form incross-section taken normal to the plane of FIGURE 1. The channel 17extends over a radius that corresponds generally to the radius aboutwhich the pipe 15 is to be bent. The radius of the surface 17 willnormally be less than the desired radius of the bend to be placed in thepipe 15 to allow for spring back of the bent pipe. The wing dies 7 and 9have semi-cylindrical surfaces 19 so that they are aligned when in theirnormal position (FIG- URE 1). When a pipe 15 is supported on the wingdies 7 and 9, the ram die 3 is actuated to move downwardly until itreaches the position shown in FIGURE 1. Immediately prior to the pipe 15being bent, it will be completely engaged around its circumference bythe die surfaces 17 and 19.

To achieve a bending of the pipe 15, the ram die 3 continues to movedownward from the position shown in FIGURE 1 to the position shown inFIGURE 2. During this movement, the wing dies 7 and 9 swing about thepivot pins 11 and 13 causing the pipe 15 to be forced into engagementwith the surface 17 of the ram die 3. Thus, the pipe 15 will be bentinto a radius that corresponds to the radius of the surface 17 of theram die 3.

During the formation of such a bend, the metal on the inside of the benddecreases in length and is placed under compression and that on theoutside of the bend increases in length and is placed in tension. Thetensile forces can cause flattening, collapsing and/or bursting of thetube along the outside of the bend during conventional bending. Inaddition, wrinkles, folds and/or blisters can occur on the inside of thebend. Blisters normally are formed when the pipe is bent with a mandrelor if laminated pipe is being bent these surface deformations occur onthe surface of the outer pipe. Wrinkles and folds occur whenconventional single layer-pipe is being bent without the use of amandrel. These deformations are caused by the stresses at the respectivepoint which stresses exceed the yield point of the metal being bent andoccur at random or unpredictable positions and times.

In accordance with the present invention, the compressive stressesacting on the inside of the bend are relieved by providing for acontrolled deformation of the metal on the inside of the bend at apredetermined location. This controlled deformation requires a volume ofmetal substantially equal to that that would be displaced by thecompression of the metal during the bending.

To form the controlled, localized deformations in the pipe 15, thesurface 17 of the ram die 3 is provided with a plurality ofcircumferentially spaced radially inwardly extending grooves 21 thatextend in planes normal to the axis of the pipe. The grooves 21 extendabout 160 angularly of the surface 17. As seen in FIGURE 4, thesegrooves are generally circular in planes taken parallel to the plane ofthe radius of the bend and decrease in radius at their peripheries.During the bending operation the metal on the inside of the pipe flowsinto the grooves 21 so that the bent pipe will be formed with a seriesof radially outwardly extending deformations or ribs 23 after it hasbeen bent (FIGURE The ribs 23 generally conform to the shape of thegrooves 21 and are made up of an amount of metal equal to that displacedby the compression of the metal due to the formation of the bend.

Another type of unsatisfactory or undesirable deformation that occurswhen bending pipe results when a bend is formed near the end of thepipe. The material on the inside of the bend flows and deforms the endof the pipe from a plane normal to the axis of the pipe to a planedisplaced from this normal position as indicated by the referencenumeral 27 in FIGURE 6. In order to maintain the straight line of 90cutoff at the end of the bent pipe it has been common practicepreviously to shear off the end of the pipe after it has been bent.Although this provides the 90 end, it should be readily obvious thatconsiderable material has been wasted. Through controlled deformation ofthe type previously noted, this additional forming step and wastage ofmaterial is obviated. FIG- URE 7 illustrates a portion of the bendingdie used to form bends in the end of the pipe. In this embodiment, thebending die 29 is formed with a surface 31 that conforms to the outerperiphery of the pipe to be bent and the radius about which the pipe isto be bent. Adjacent the end of the pipe, however, a localized surfacedeformation or relief 33 is formed in the bending die surface 31 toprovide a space accommodating the end of the pipe without deforming itout of square.

It is to be understood that the foregoing description merely relates toa preferred embodiment the invention may take but that various changesand modifications may be made without departing from the spirit andscope of the invention, as defined by the appended claims.

I claim:

1. In a tube bending apparatus, a bend die, a pairof wing dies supportedadjacent the bend die to cooperate with the bend die in bending a tube,said bend die having a convexly curved periphery facing said wing dies,said wing dies having aligned substantially straight peripheries facingthe bend die periphery, each of said peripheries being provided with asubstantially semi-circular channel and said channels defining a crosssectional space to receive a tube for bending, the channels in said wingdies being on the outside of the bend formed in the tube and each beingof a substantially smooth and continuous surface along its length, thechannel in the bend die being on the inside of the bend formed in thetube and having a plurality of grooves formed therein spaced from eachother along the length of the channel and each extending transversely tothe length of the channel, said grooves serving to form outwardlyprojecting stress relieving ribs on the inside of the bend of a tube bythe apparatus.

2. The method of forming an arcuate bend in a hollow tubular articlehaving substantially uniform Wall thickness and preventing undesirablesurface deformations due to the stresses induced in the material of thearticle by the bending without use of a mandrel comprising the steps ofapplying bending force transverse to the length of the tubular articleto permanently deform the tubular article into the arcuate bend andemploying the compressive stresses generated in the material on theinside of the bend by bending of the article to permanently deform thematerial into a plurality of angularly spaced outwardly projecting ribsextending in planes transverse to the center line of the tubular articleat preselected and predetermined locations on the inner periphery onlyof the bend.

3. The method as set forth in claim 2 wherein the volume of the materialforming the ribs is substantially equal to the amount of materialdisplaced by compressive stresses during the formation of the bend.

4. The method as set forth in claim 2 wherein the compressive stressesgenerated on the inside of the bend are utilized to cause the materialto fiow into grooves in a die surface contacting the article on theinside of the bend, said grooves serving to form and locate said ribs.

5. In apparatus for bending a tube and having a reciproeating ram forapplying bending force to a tube, a die body for attachment to andreciprocation with said ram, said die body having a convex peripheryprovided with a substantially semi-circular cross section channel forreceiving and engaging a substantial length of a tube to be bent, saidchannel engaging the tube on the inside of the bend formed in the tube,said body periphery having a plurality of grooves formed therein locatedin the channel and spaced from each other along the length of thechannel, said grooves each extending transversely to the length of thechannel and along a major portion of the substantially semi-circularwidth of the channel and serving to form outwardly projecting stressrelieving ribs on the inside of the bend of a tube bent by the die whichlie in planes transverse to the axis of the tube.

References Cited UNITED STATES PATENTS 1,197,271 10/1916 Dieckmann 723692,406,838 11/1946 Kepler 72-369 361,487 4/1887 Brownson 72-382 3,240,0483/1966 Callendar 72369 FOREIGN PATENTS 1,167,630 4/ 1964 Germany.

CHARLES W. LANHAM, Primary Examiner B. J. MUSTAIKIS, Assistant ExaminerUS. Cl. X.R.

